----- Original Message ----
> From: Ross Walker <rswwalker@xxxxxxxxx>
> To: CentOS mailing list <centos@xxxxxxxxxx>
> Cc: CentOS mailing list <centos@xxxxxxxxxx>
> Sent: Thu, February 11, 2010 12:30:43 PM
> Subject: Re: disk I/O problems with LSI Logic RAID controller
>
> On Feb 11, 2010, at 2:46 AM, Andrzej Szymanski
> wrote:
>
> > The iostat output looks good to me for the RAID setup you have.
> > I'd look for the problem in a different place:
> >
> > note the output of
> > cat /proc/sys/vm/dirty_background_ratio
> > and try
> > echo 1 > /proc/sys/vm/dirty_background_ratio
> > whether it helps.
>
> Excellent suggestion, on machines with lots of memory the default
> dirty background ratio is way too big, and needs to be tuned down for
> both data integrity in the event of a system failure and performance
> of the underlying storage configuration.
>
> Take into account the RAID setup, write-back cache size and time it
> takes to empty it to disk and pick a dirty background ratio somewhere
> in between.
You nailed it. I tweaked the dirty_background ratio and changed the scheduller to deadline and now it works way better. it still see-saws a bit but the utilization never dropts to zero.
Thanks you for your help.
Fer
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